1. Field of the Invention
Generally, this invention relates to primary lithium batteries for use in self-contained self-powered devices (SSPD) such as radio frequency identification tags, PCMCIA cards, and smart cards. More particularly, this invention relates to improved component design and packaging for flexible lithium batteries adapted for use in self-contained self-powered devices.
2. Cross-Reference
The invention disclosed and claimed herein is related to the inventions disclosed and claimed in applications Ser. Nos. 08/614,982 and 08/727,096, now abandoned which were filed on Mar. 12, 1996 and Oct. 8, 1996, respectively, and which are assigned to the same assignee as the instant invention.
3. Description of Prior Art
Self-contained self-powered portable devices (SSPD) encompass an increasingly large market of mobile communication and computing products such as radio frequency identification (RF-ID) tags, PCMCIA cards, and smart cards. For a battery to be useable in such applications, it must meet several demanding characteristics. First, for safety reasons, the battery must be constructed of all solid components while still being flexible and compact. Secondly, the battery should exhibit similar conductivity characteristics to primary batteries with liquid electrolytes, i.e., deliver high energy density and specific energy with low rates of self-discharge. Thirdly, the battery should be readily manufacturable in a manner that yields a battery that is both reliable and cost-efficient. Finally, the battery must also be able to maintain a necessary minimum level of conductivity at sub-ambient temperatures.
Primary (non-rechargeable) lithium batteries have been found particularly well suited for meeting these requirements. Such batteries can be constructed of all solid components, including the electrolyte in order to avoid the hazard of electrolyte leakage. Such electrolytes have been formed as a solid polymer electrolyte composed of a polymer membrane having a suitable electrolyte contained within its matrix.
The use of polyethylene oxide (PEO) as a solid polymer electrolyte membrane material for a flexible lithium battery has been proposed in the prior art. Solid electrolytes formed with this material have exhibited satisfactory ambient temperature conductivity, and provide good performance at sub-ambient temperatures when used to deliver short current pulses of about thirty .mu.A/cm.sup.2 per for durations of up to about 10 milliseconds. Also, polyethylene oxide-based lithium batteries can be readily manufactured using well-established fabrication techniques, yielding a flexible battery that is both reliable and cost-efficient.
While batteries with polyethylene oxide-based electrolyte membranes have achieved many design criteria for SSPD applications, further improvements, such as minimizing the thickness of the electrolyte membrane, or eliminating it altogether, and minimizing or eliminating inactive materials would be desirable and would result in batteries having higher energy densities.